1. Field of the Invention
The present invention relates to a purine derivative having a cyclopropane ring, a process for preparing the same, and a process for preparing a cyclopropane ring-cleaved purine derivative from the purine derivative having a cyclopropane ring. The present invention also relates to a process for preparing a cyclopropane ring-cleaved compound.
2. Discussion of the Related Art
Conventionally, as to preparation process for purine derivatives useful for preparation intermediates for antiviral agents, there can be cited, for instance, a process disclosed in Japanese Patent Laid-Open No. Hei 3-120279. However, when the purine derivative is prepared from the preparation intermediates in the above preparation processes, its yield is as low as about 20 to about 40%. In addition, since extremely complicated procedures are necessitated in order to prepare the above preparation intermediates, there is a defect that the purine derivatives cannot be readily prepared as a consequence.
Therefore, recently, a development of a preparation intermediate which can be used in a process which can readily prepare a cyclopropane ring-cleaved purine derivative in a high yield and at high purity has been in demand.
In addition, there has been known to prepare a cyclopropane ring-cleaved compound by a process comprising hydrogenating a compound having a cyclopropane ring in the presence of a metal catalyst by the action of hydrogen gas as a hydrogen source; and cleaving the cyclopropane ring by reduction.
However, in this process, since it has been necessitated to pressurize the reaction system with hydrogen gas to a pressure of 3 to 5 kgf/cm2 upon hydrogenation, there arise such defects that the desired cyclopropane ring-cleaved compound has a low yield owing to the presence of large amounts of by-products in addition to the lack of operability and safety.
In view of the problems in the prior art, an object of the present invention is to provide a process for readily preparing a cyclopropane ring-cleaved purine derivative in a high yield and at high purity, a purine derivative having a cyclopropane ring which can be suitably used in the above process, and a process for preparing the purine derivative having a cyclopropane ring.
Another object of the present invention is to provide a process for preparing a cyclopropane ring-cleaved compound with excellent operability and safety in a high yield.
These and other objects of the present invention will be apparent from the following description.
The present invention pertains to the following:
(1) a purine derivative having a cyclopropane ring represented by the formula (I): 
xe2x80x83wherein A is xe2x80x94CH2xe2x80x94 group or xe2x80x94COxe2x80x94 group; X1 is hydrogen atom, a halogen atom, an alkoxy group having 1 to 10 carbon atoms, or hydroxyl group; each of X2, X3, and X4 is independently hydrogen atom or a halogen atom; R1 is hydrogen atom, a halogen atom, or a protected or unprotected amino group; and each of R2 and R3 is independently hydrogen atom, a substituted or unsubstituted alkyl group having 1 to 7 carbon atoms, a substituted or unsubstituted aralkyl group having 7 to 11 carbon atoms, or a substituted or unsubstituted acyl group having 1 to 7 carbon atoms, with proviso that in a case where A is xe2x80x94COxe2x80x94 group, neither R2 nor R3 is a substituted or unsubstituted acyl group having 1 to 7 carbon atoms, and each of X3 and X4 is independently a halogen atom;
(2) the purine derivative having a cyclopropane ring according to item (1) above, wherein the purine derivative having a cyclopropane ring represented by the formula (I) is a compound represented by the formula (II): 
xe2x80x83wherein each of X13 and X14 is independently a halogen atom; each of R4 and R5 is independently hydrogen atom, a substituted or unsubstituted alkyl group having 1 to 7 carbon atoms, or a substituted or unsubstituted aralkyl group having 7 to 11 carbon atoms; and X1, X2, and R1 are the same as defined above;
(3) the purine derivative having a cyclopropane ring according to item (1) above, wherein the purine derivative having a cyclopropane ring represented by the formula (I) is a compound represented by the formula (III): 
xe2x80x83wherein X1, X2, X3, X4, R1, R2, and R3 are the same as defined above;
(4) the purine derivative having a cyclopropane ring according to item (3) above, wherein the purine derivative having a cyclopropane ring represented by the formula (III) is a compound represented by the formula (IV): 
xe2x80x83wherein each of X5 and X6 is independently a halogen atom; and X1, X2, R1, R2, and R3 are the same as defined above;
(5) the purine derivative having a cyclopropane ring according to item (3) or (4) above, wherein X1 is chlorine atom;
(6) the purine derivative having a cyclopropane ring according to any one of items (3) to (5) above, wherein each of R2 and R3 is hydrogen atom;
(7) the purine derivative having a cyclopropane ring according to any one of items (3) to (5) above, wherein each of R2 and R3 is acetyl group;
(8) a process for preparing a purine derivative having a cyclopropane ring represented by the formula (II): 
xe2x80x83wherein X1 is hydrogen atom, a halogen atom, an alkoxy group having 1 to 10 carbon atoms, or hydroxyl group; X2 is hydrogen atom or a halogen atom; each of X13 and X14 is independently a halogen atom; R1 is hydrogen atom, a halogen atom, or a protected or unprotected amino group; and each of R4 and R5 is independently hydrogen atom, a substituted or unsubstituted alkyl group having 1 to 7 carbon atoms, or a substituted or unsubstituted aralkyl group having 7 to 11 carbon atoms,
comprising reacting a malonic acid derivative represented by the formula (V): 
xe2x80x83wherein each of X7, X13, and X14 is independently a halogen atom; and R4 and R5 are the same as defined above, with a purine compound represented by the formula (VI): 
xe2x80x83wherein X1, X2, and R1 are the same as defined above;
(9) a process for preparing a purine derivative having a cyclopropane ring represented by the formula (IIIa): 
xe2x80x83wherein X1 is hydrogen atom, a halogen atom, an alkoxy group having 1 to 10 carbon atoms, or hydroxyl group; X2 is hydrogen atom or a halogen atom; each of X13 and X14 is independently a halogen atom; and R1 is hydrogen atom, a halogen atom, or a protected or unprotected amino group,
comprising reacting a dicarboxylic acid-based compound represented by the formula (VII): 
xe2x80x83wherein each of R6 and R7 is independently a substituted or unsubstituted alkyl group having 1 to 7 carbon atoms; and X1, X2, X13, X14 and R1 are the same as defined above, with a metal hydride;
(10) a process for preparing a purine derivative having a cyclopropane ring represented by the formula (IIIc): 
xe2x80x83wherein X1 is hydrogen atom, a halogen atom, an alkoxy group having 1 to 10 carbon atoms, or hydroxyl group; each of X2, X3, and X4 is independently hydrogen atom or a halogen atom; R1 is hydrogen atom, a halogen atom, or a protected or unprotected amino group; and each of R8""s is independently a substituted or unsubstituted alkyl group having 1 to 7 carbon atoms or a substituted or unsubstituted aralkyl group having 7 to 11 carbon atoms,
comprising reacting a purine derivative having a cyclopropane ring represented by the formula (IIIb): 
xe2x80x83wherein X1, X2, X3, X4, and R1 are the same as defined above,
with an alkylating agent represented by the formula (VIII):
R8xe2x80x94X8xe2x80x83xe2x80x83(VIII)
wherein X8 is chlorine atom, bromine atom, or iodine atom; and R8 is the same as defined above;
(11) a process for preparing a purine derivative having a cyclopropane ring represented by the formula (IIId): 
xe2x80x83wherein X1 is hydrogen atom, a halogen atom, an alkoxy group having 1 to 10 carbon atoms, or hydroxyl group; each of X2, X3, and X4 is independently hydrogen atom or a halogen atom; R1 is hydrogen atom, a halogen atom, or a protected or unprotected amino group; and each of R9""s is independently a substituted or unsubstituted acyl group having 1 to 7 carbon atoms,
comprising reacting a purine derivative having a cyclopropane ring represented by the formula (IIIb): 
xe2x80x83wherein X1, X2, X3, X4, and R1 are the same as defined above,
with a compound represented by the formula (IX):
R9xe2x80x94X9xe2x80x83xe2x80x83(IX)
wherein X9 is hydroxyl group, chlorine atom, bromine atom, or xe2x80x94OR9 group; and R9 is the same as defined above.
(12) a process for preparing a cyclopropane ring-cleaved purine derivative represented by the formula (X): 
xe2x80x83wherein A is xe2x80x94CH2xe2x80x94 group or xe2x80x94COxe2x80x94 group; X10 is hydrogen atom, an alkoxy group having 1 to 10 carbon atoms, or hydroxyl group; and each of R2 and R3 is independently hydrogen atom, a substituted or unsubstituted alkyl group having 1 to 7 carbon atoms, a substituted or unsubstituted aralkyl group having 7 to 11 carbon atoms, or a substituted or unsubstituted acyl group having 1 to 7 carbon atoms; and R10 is hydrogen atom or a protected or unprotected amino group, with proviso that in a case where A is xe2x80x94COxe2x80x94 group, neither R2 nor R3 is a substituted or unsubstituted acyl group having 1 to 7 carbon atoms, comprising hydrogenating a purine derivative having a cyclopropane ring represented by the formula (I): 
xe2x80x83wherein X1 is hydrogen atom, a halogen atom, an alkoxy group having 1 to 10 carbon atoms, or hydroxyl group; each of X2, X3, and X4 is independently hydrogen atom or a halogen atom; R1 is hydrogen atom, a halogen atom, or a protected or unprotected amino group; and A, R2 and R3 are the same as defined above, with proviso that in a case where A is xe2x80x94COxe2x80x94 group, neither R2 nor R3 is a substituted or unsubstituted acyl group having 1 to 7 carbon atoms, and each of X3 and X4 is independently a halogen atom;
(13) a process for preparing a cyclopropane ring-cleaved compound represented by the formula (XII): 
xe2x80x83wherein A is xe2x80x94CH2xe2x80x94 group or xe2x80x94COxe2x80x94 group; B is a nitrogen-containing heterocyclic ring; and each of R11 and R12 is independently hydrogen atom, a substituted or unsubstituted alkyl group having 1 to 7 carbon atoms, a substituted or unsubstituted aralkyl group having 7 to 11 carbon atoms, or a substituted or unsubstituted acyl group having 1 to 7 carbon atoms, with proviso that in a case where A is xe2x80x94COxe2x80x94 group, neither R11 nor R12 is a substituted or unsubstituted acyl group having 1 to 7 carbon atoms,
comprising reacting a compound having a cyclopropane ring represented by the formula (XI): 
xe2x80x83wherein each of X11 and X12 is independently hydrogen atom or a halogen atom; and A, B, R11, and R12 are the same as defined above, with proviso that in a case where A is xe2x80x94COxe2x80x94 group, neither R11 nor R12 is a substituted or unsubstituted acyl group having 1 to 7 carbon atoms, and each of X11 and X12 is independently a halogen atom,
with formic acid or a formate in the presence of a catalyst;
(14) the process according to item (13) above, wherein the catalyst is at least one substance selected from the group consisting of palladium, platinum, nickel, and compounds of one of these elements; and
(15) the process according to item (13) or (14) above, wherein the formate is an alkali metal formate.
As mentioned above, the purine derivative having a cyclopropane ring of the present invention is a compound represented by the formula (I): 
wherein A is xe2x80x94CH2xe2x80x94 group or xe2x80x94COxe2x80x94 group; X1 is hydrogen atom, a halogen atom, an alkoxy group having 1 to 10 carbon atoms, or hydroxyl group; each of X2, X3, and X4 is independently hydrogen atom or a halogen atom; R1 is hydrogen atom, a halogen atom, or a protected or unprotected amino group; each of R2 and R3 is independently hydrogen atom, a substituted or unsubstituted alkyl group having 1 to 7 carbon atoms, a substituted or unsubstituted aralkyl group having 7 to 11 carbon atoms, or a substituted or unsubstituted acyl group having 1 to 7 carbon atoms, with proviso that in a case where A is xe2x80x94COxe2x80x94 group, neither R2 nor R3 is a substituted or unsubstituted acyl group having 1 to 7 carbon atoms, and each of X3 and X4 is independently a halogen atom.
In the formula (I), A is xe2x80x94CH2xe2x80x94 group or xe2x80x94COxe2x80x94 group.
X1 is hydrogen atom, a halogen atom, an alkoxy group having 1 to 10 carbon atoms, or hydroxyl group. Examples of the halogen atom include fluorine atom, chlorine atom, bromine atom, and iodine atom, among which a preference is given to chlorine atom, bromine atom, and iodine atom.
Examples of the alkoxy group having 1 to 10 carbon atoms include methoxy group, ethoxy group, propoxy group, benzyloxy group, 2-methyl-2-propoxy group, cyclopentyloxy group, cyclohexyloxy group, and the like.
Each of X2, X3, and X4 is independently hydrogen atom or a halogen atom. Examples of the halogen atom include fluorine atom, chlorine atom, bromine atom, and iodine atom, among which a preference is given to chlorine atom, bromine atom, and iodine atom, with proviso that in a case where A is xe2x80x94COxe2x80x94 group, each of X3 and X4 is independently a halogen atom.
R1 is hydrogen atom, a halogen atom, or a protected or unprotected amino group. Examples of the halogen atom include fluorine atom, chlorine atom, bromine atom, and iodine atom.
Concrete examples of the protected amino group include formylamino group, acetylamino group, benzylamino group, dimethylaminomethyleneamino group, benzyloxycarbonylamino group, and the like.
Each of R2 and R3 is independently hydrogen atom, a substituted or unsubstituted alkyl group having 1 to 7 carbon atoms, a substituted or unsubstituted aralkyl group having 7 to 11 carbon atoms, or a substituted or unsubstituted acyl group having 1 to 7 carbon atoms, with proviso that in a case where A is xe2x80x94COxe2x80x94 group, neither R2 nor R3 is a substituted or unsubstituted acyl group having 1 to 7 carbon atoms.
Examples of the alkyl group having 1 to 7 carbon atoms include methyl group, ethyl group, propyl group, isopropyl group, 2-methylpropyl group, and the like.
Examples of the aralkyl group having 7 to 11 carbon atoms include benzyl group, and the like.
Examples of the acyl group having 1 to 7 carbon atoms include formyl group, acetyl group, benzoyl group, pivaloyl group, and the like.
Examples of the substituent which may be carried by the alkyl group, the aralkyl group, and the acyl group include alkoxy groups having 1 to 6 carbon atoms, such as methoxy group and phenoxy group; hydroxy group; nitro group; amino group; halogen atoms, such as chlorine atom; cyano group, and the like.
In one embodiment where A is xe2x80x94COxe2x80x94 group in the purine derivative having a cyclopropane ring of the present invention represented by the formula (I), the compound is represented by the formula (II): 
wherein each of X13 and X14 is independently a halogen atom; each of R4 and R5 is independently hydrogen atom, a substituted or unsubstituted alkyl group having 1 to 7 carbon atoms, or a substituted or unsubstituted aralkyl group having 7 to 11 carbon atoms; and X1, X2, and R1 are the same as defined above.
In each of R4 and R5 above, the substituted or unsubstituted alkyl group having 1 to 7 carbon atoms and the substituted or unsubstituted aralkyl group having 7 to 11 carbon atoms may be the same ones as those exemplified for the substituted or unsubstituted alkyl group having 1 to 7 carbon atoms and the substituted or unsubstituted aralkyl group having 7 to 11 carbon atoms described in R2 and R3 of the formula (I).
In the formula (II), it is desired that each of X1, X13, and X14 is chlorine atom, bromine atom, or iodine atom; X2 is hydrogen atom; each of R4 and R5 is an alkyl group having 1 to 5 carbon atoms, or hydrogen atom; and R1 is a protected or unprotected amino group. Examples of the alkyl group having 1 to 5 carbon atoms include methyl group, ethyl group, propyl group, isopropyl group, butyl group, pentyl group, and the like.
In addition, in the formula (II), when R1 is a protected or unprotected amino group, examples of the protected group which may be carried by amino group include an acyl group having 1 to 7 carbon atoms, a group represented by CH3xe2x80x94N(CH3)xe2x80x94CHxe2x95x90, and the like. Examples of the acyl group having 1 to 7 carbon atoms include formyl group, acetyl group, pivaloyl group, benzoyl group, and the like.
The purine derivative having a cyclopropane ring represented by the formula (II) can be prepared by a process comprising reacting a malonic acid derivative represented by the formula (V): 
wherein each of X7, X13, and X14 is independently a halogen atom; and each of R4 and R5 is independently hydrogen atom, a substituted or unsubstituted alkyl group having 1 to 7 carbon atoms, or a substituted or unsubstituted aralkyl group having 7 to 11 carbon atoms, with a purine compound represented by the formula (VI): 
wherein X1 is hydrogen atom, a halogen atom, an alkoxy group having 1 to 10 carbon atoms, or hydroxyl group; X2 is hydrogen atom or a halogen atom; and R1 is hydrogen atom, a halogen atom, or a protected or unprotected amino group.
In the present invention, the reaction of the malonic acid derivative represented by the formula (V) with the purine compound represented by the formula (VI) can be carried out by a process, for instance, comprising adding a purine compound represented by the formula (VI) in advance to a solvent and stirring the resulting mixed solution, and subsequently adding a malonic acid derivative represented by the formula (V) to the resulting mixture.
In the formula (V), it is desired that each of X7, X13, and X14 is chlorine atom, bromine atom, or iodine atom; and each of R4 and R5 is a substituted or unsubstituted alkyl group having 1 to 5 carbon atoms, or hydrogen atom.
In the formula (VI), it is desired that X1 is chlorine atom, bromine atom, or iodine atom; X2 is hydrogen atom; and R1 is a protected or unprotected amino group.
As to the solvents, there can be cited, for instance, N,N-dimethylformamide, N-methylpyrrolidone, dimethylsulfoxide, and the like, among which N,N-dimethylformamide and dimethylsulfoxide are favorably used from the viewpoints of reactivity and economic advantages.
It is desired that the amount of the solvent is usually from about 500 to about 10000 parts by weight, based on 100 parts by weight of the purine compound represented by the formula (VI).
Incidentally, in the present invention, it is desired that the reaction of the malonic acid derivative represented by the formula (V) with the purine compound represented by the formula (VI) is carried out in the presence of a base having weak nucleophilic property. Typical examples of the base having weak nucleophilic property include alkali metal carbonates.
Examples of the alkali metal carbonates include potassium carbonate, sodium carbonate, rubidium carbonate, cesium carbonate, and the like, among which potassium carbonate can be favorably used from the viewpoint of the reactivity.
It is desired that the amount of the alkali metal carbonate is usually 0.5 mol or more, preferably one mol or more, per one mol of the purine compound represented by the formula (VI) in order to expedite the progress of the reaction, and that the amount of the alkali metal carbonate is 20 mol or less, preferably 5 mol or less, per one mol of the purine compound represented by the formula (VI), from the viewpoint of economic advantages.
The alkali metal carbonate can be used by adding to the solvent together with the purine compound represented by the formula (VI).
It is desired that the amount of the malonic acid derivative represented by the formula (V) is usually one mol or more, preferably 1.1 mol or more, per one mol of the purine compound represented by the formula (VI), since one mol of the malonic acid derivative is theoretically needed to one mol of the purine compound. It is also desired that the amount of the malonic acid derivative is 50 mol or less, preferably 5 mol or less, per one mol of the purine compound represented by the formula (VI), from the viewpoint of economic advantages.
The malonic acid derivative represented by the formula (V) can be readily prepared by a process, for instance, disclosed in U.S. Pat. No. 3,495,012.
The atmosphere in which the reaction of the malonic acid derivative represented by the formula (V) with the purine compound represented by the formula (VI) is carried out is not limited to specified ones, and the atmosphere may be preferably air, or an inert gas atmosphere such as nitrogen gas, and argon gas. It is also desired that the reaction temperature is usually from about xe2x80x9410xc2x0 to about 100xc2x0 C., preferably from about 0xc2x0 to about 60xc2x0 C.
The reaction time cannot be absolutely determined because the reaction time can differ depending upon the reaction temperature, and the like. The reaction time may be preferably a length of time sufficient to terminate the reaction, and the reaction time is usually from 0.5 to 5 hours or so.
The termination of the reaction can be confirmed, for instance, by high-performance liquid chromatography, or the like.
After the termination of reaction, the resulting purine derivative having a cyclopropane ring represented by the formula (II) can be isolated by carrying out such procedures including filtration, precipitation, washing, concentration, and the like.
Thus, the purine derivative having a cyclopropane ring represented by the formula (II) can be readily prepared.
In another embodiment where A is xe2x80x94CH2xe2x80x94 group in the purine derivative having a cyclopropane ring in the formula (I), the compound is represented by the formula (III): 
wherein X1, X2, X3, X4, R1, R2, and R3 are the same as defined above.
In the present invention, among the purine derivatives having a cyclopropane ring represented by the formula (III), the purine derivative having a cyclopropane ring represented by the formula (IV): 
wherein each of X5 and X6 is independently a halogen atom; and X1, X2, R1, R2, and R3 are the same as defined above, is preferable. Among them, the compounds where X1 is chlorine atom, and the compounds where each of R1 and R2 is hydrogen atom or acetyl group are particularly favorably used as preparation intermediates for antiviral agents.
In X5 and X6 above, examples of the halogen atom include fluorine atom, chlorine atom, bromine atom, and iodine atom, among which a preference is given to chlorine atom, bromine atom, and iodine atom.
A compound where each of R2 and R3 is hydrogen atom and each of X3 and X4 is a halogen atom in the purine derivative having a cyclopropane ring represented by the formula (III), namely a purine derivative having a cyclopropane ring represented by the formula (IIIa): 
wherein X1, X2, X13, X14, and R1 are the same as defined above,
can be prepared by a process comprising reacting a dicarboxylic acid-based compound represented by the formula (VII): 
wherein each of R6 and R7 is independently a substituted or unsubstituted alkyl group having 1 to 7 carbon atoms; and X1, X2, X13, X14, and R1 are the same as defined above, with a metal hydride.
In each of R6 and R7, the substituted or unsubstituted alkyl group having 1 to 7 carbon atoms may be the same ones as those exemplified for the substituted or unsubstituted alkyl group having 1 to 7 carbon atoms described in R2 and R3 of the formula (I).
The reaction of the dicarboxylic acid-based compound represented by the formula (VII) with the metal hydride can be carried out by a process, for instance, comprising dissolving or suspending a dicarboxylic acid-based compound represented by the formula (VII) in a solvent, and adding a metal hydride to the resulting mixture.
The dicarboxylic acid-based compound represented by the formula (VII) can be prepared by a process disclosed, for instance, in Japanese Patent Laid-Open No. Hei 3-120279.
Examples of the metal hydride include sodium borohydride, borane, lithium aluminum hydride, diisobutylaluminum hydride, lithium borohydride, and the like.
Since 4 mol of hydride ions is theoretically required to one mol of the dicarboxylic acid-based compound represented by the formula (VII), it is desired that the amount of the metal hydride is adjusted such that the amount of the hydride ions is 4 mol or more, preferably 6 mol or more, to one mol of the dicarboxylic acid-based compound represented by the formula (VII). From the viewpoint of economic advantages, it is desired that the amount of the metal hydride is adjusted such that the amount of the hydride ions is 30 mol or less, preferably 20 mol or less, to one mol of the dicarboxylic acid-based compound represented by the formula (VII).
Examples of the solvent include polar solvents such as N,N-dimethylformamide and 1,3-dimethyl-2-imidazolidinone; alcohols such as methanol, ethanol, 2-propanol, and 2-methyl-2-propanol; ethers such as tetrahydrofuran, and the like. It is desired that the amount of the solvent is adjusted such that the amount of the dicarboxylic acid-based compound represented by the formula (VII) is usually from 1 to 50 parts by weight, based on 100 parts by weight of the solvent.
It is desired that the temperature upon the reaction of the dicarboxylic acid-based compound represented by the formula (VII) with the metal hydride is usually 0xc2x0 to 50xc2x0 C. or so. The atmosphere may be an air or an inert gas such as nitrogen gas.
The reaction time cannot be absolutely determined because the reaction time can differ depending upon the reaction temperature, and the like. The reaction time may be preferably a length of time sufficient to terminate the reaction, and the reaction time is usually from 0.5 to 5 hours or so. The termination of the reaction can be confirmed, for instance, by high-performance liquid chromatography, or the like.
A compound where each of R2 and R3 is a substituted or unsubstituted alkyl group having 1 to 7 carbon atoms or a substituted or unsubstituted aralkyl group having 7 to 11 carbon atoms in the purine derivative having a cyclopropane ring represented by the formula (III), namely a purine derivative having a cyclopropane ring represented by the formula (IIIc): 
wherein each of R8+ is independently a substituted or unsubstituted alkyl group having 1 to 7 carbon atoms or a substituted or unsubstituted aralkyl group having 7 to 11 carbon atoms; and X1, X2, X3, X4, and R1 are the same as defined above,
can be prepared by a process comprising reacting a purine derivative having a cyclopropane ring represented by the formula (IIIb): 
xe2x80x83wherein X1, X2, X3, X4, and R1 are the same as defined above,
with an alkylating agent represented by the formula (VIII):
R8xe2x80x94X8xe2x80x83xe2x80x83(VIII)
wherein X8 is chlorine atom, bromine atom, or iodine atom; and R8 is the same as defined above.
In R8 above, the substituted or unsubstituted alkyl group having 1 to 7 carbon atoms and the substituted or unsubstituted aralkyl group having 7 to 11 carbon atoms may be the same ones as those exemplified for the substituted or unsubstituted alkyl group having 1 to 7 carbon atoms and the substituted or unsubstituted aralkyl group having 7 to 11 carbon atoms described in R2 and R3 of the formula (I).
The reaction of the purine derivative having a cyclopropane ring represented by the formula (IIIb) with the alkylating agent represented by the formula (VIII) can be carried out by a process, for instance, comprising dissolving a purine derivative having a cyclopropane ring represented by the formula (IIIb) in a solvent, and adding an alkylating agent to the resulting mixture.
Since 2 mol of the alkylating agent represented by the formula (VIII) is theoretically required to one mol of the purine derivative having a cyclopropane ring represented by the formula (IIIb), it is desired that the amount of the alkylating agent is 2 mol or more, preferably 2.2 mol or more, per one mol of the purine derivative having a cyclopropane ring represented by the formula (IIIb). From the viewpoint of economic advantages, it is desired that the amount of the alkylating agent is 10 mol or less, preferably 4 mol or less, per one mol of the purine derivative having a cyclopropane ring represented by the formula (IIIb).
Examples of the solvent include esters such as ethyl acetate; ethers such as tetrahydrofuran; nitriles such as acetonitrile; aromatic hydrocarbons such as toluene, and the like. It is desired that the amount of the solvent is adjusted such that the amount of the purine derivative having a cyclopropane ring represented by the formula (IIIb) is usually from 1 to 50 parts by weight, based on 100 parts by weight of the solvent.
It is desired that the temperature upon the reaction of the purine derivative having a cyclopropane ring represented by the formula (IIIb) with the alkylating agent represented by the formula (VIII) is usually 10xc2x0 to 80xc2x0 C. or so. The atmosphere may be an air or an inert gas such as nitrogen gas.
The reaction time cannot be absolutely determined because the reaction time can differ depending upon the reaction temperature, and the like. The reaction time may be preferably a length of time sufficient to terminate the reaction, and the reaction time is usually from 1.5 to 8 hours or so. The termination of the reaction can be confirmed, for instance, by high-performance liquid chromatography, or the like.
A compound where each of R2 and R3 is a substituted or unsubstituted acyl group having 1 to 7 carbon atoms in the purine derivative having a cyclopropane ring represented by the formula (III), namely a purine derivative having a cyclopropane ring represented by the formula (IIId): 
wherein each of R9""s is independently a substituted or unsubstituted acyl group having 1 to 7 carbon atoms; and X1, X2, X3, X4, and R1 are the same as defined above,
can be prepared by a process comprising reacting a purine derivative having a cyclopropane ring represented by the formula (IIIb) with a compound represented by the formula (IX):
xe2x80x83R9xe2x80x94X9xe2x80x83xe2x80x83(IX)
wherein X9 is hydroxyl group, chlorine atom, bromine atom, or xe2x80x94OR9 group; and R9 is the same as defined above.
In R9 above, the substituted or unsubstituted acyl group having 1 to 7 carbon atoms may be the same ones as those exemplified for the substituted or unsubstituted acyl group having 1 to 7 carbon atoms described in R2 and R3 of the formula (I).
X9 is hydroxyl group, chlorine atom, bromine atom, or xe2x80x94OR9 group; and R9 is the same as defined above.
The reaction of the purine derivative having a cyclopropane ring represented by the formula (IIIb) with the compound represented by the formula (IX) can be carried out by a process, for instance, comprising suspending a purine derivative having a cyclopropane ring represented by the formula (IIIb) in a solvent, adding a base to the resulting suspension, and subsequently adding a compound represented by the formula (IX) to the resulting mixture.
Since 2 mol of the compound represented by the formula (IX) is theoretically required to one mol of the purine derivative having a cyclopropane ring represented by the formula (IIIb), it is desired that the amount of the compound represented by the formula (XI) is 2 mol or more, preferably 2.2 mol or more, per one mol of the purine derivative having a cyclopropane ring represented by the formula (IIIb). From the viewpoint of economic advantages, it is desired that the amount of the compound represented by the formula (XI) is 10 mol or less, preferably 4 mol or less, per one mol of the purine derivative having a cyclopropane ring represented by the formula (IIIb).
Examples of the base include nitrogen-containing heterocyclic compounds such as pyridine, 4-dimethylaminopyridine, imidazole, and diazabicycloundecene; tertiary amines such as triethylamine and diisopropylethylamine, and the like. Those bases may be used alone or in an admixture thereof. It is desired that the amount of the base is equal to or more than the stoichiometric amount to one mol of the purine derivative having a cyclopropane ring represented by the formula (IIIb), namely 2 mol or more, preferably 2.2 mol or more.
Examples of the solvent include esters such as ethyl acetate; ethers such as tetrahydrofuran; nitrites such as acetonitrile; aromatic hydrocarbons such as toluene, and the like. It is desired that the amount of the solvent is adjusted such that the amount of the purine derivative having a cyclopropane ring represented by the formula (IIIb) is usually from 1 to 50 parts by weight, based on 100 parts by weight of the solvent.
It is desired that the temperature upon the reaction of the purine derivative having a cyclopropane ring represented by the formula (IIIb) with the compound represented by the formula (IX) is usually 0xc2x0 to 80xc2x0 C. or so. The atmosphere may be an air or an inert gas such as nitrogen gas.
The reaction time cannot be absolutely determined because the reaction time can differ depending upon the reaction temperature, and the like. The reaction time may be preferably a length of time sufficient to terminate the reaction, and the reaction time is usually from 0.5 to 5 hours or so. The termination of the reaction can be confirmed, for instance, by high-performance liquid chromatography, or the like.
The purine derivative having a cyclopropane ring represented by the formula (I) as described above is a novel compound, and it can be favorably used for preparation intermediates for a cyclopropane ring-cleaved purine derivative represented by the formula (X): 
wherein X10 is hydrogen atom, an alkoxy group having 1 to 10 carbon atoms, or hydroxyl group; R10 is hydrogen atom or a protected or unprotected amino group; and A, R2, and R3 are the same as defined above, with proviso that in a case where A is xe2x80x94COxe2x80x94 group, neither R2 nor R3 is a substituted or unsubstituted acyl group having 1 to 7 carbon atoms, which can be used for preparation intermediates for antiviral agents as disclosed in, for instance, xe2x80x9cNucleoside Nucleotide,xe2x80x9d 15[5] (1996), 981-994; Japanese Examined Patent Publication No. Hei 5-86792, and the like.
In X10 above, the alkoxy group having 1 to 10 carbon atoms may be the same ones as those exemplified for the alkoxy group having 1 to 10 carbon atoms described in X1 of the formula (I).
In R10 above, the protected or unprotected amyl group may be the same ones as those exemplified for the protected or unprotected amyl group described in R1 of the formula (I).
In the present invention, the cyclopropane ring-cleaved purine derivative represented by the formula (X) can be prepared by a process comprising hydrogenating a purine derivative having a cyclopropane ring represented by the formula (I).
There are, for instance, two embodiments of processes for hydrogenating a purine derivative having a cyclopropane ring represented by the formula (I).
Embodiment (A): a process for catalytically reducing a purine derivative having a cyclopropane ring represented by the formula (I).
Embodiment (B): a process for reacting a purine derivative having a cyclopropane ring represented by the formula (I) with formic acid or a formate.
Among Embodiments (A) and (B), Embodiment (B) is preferably employed from the viewpoints of reactivity and operability.
In Embodiment (A), the catalytic reduction of the purine derivative having a cyclopropane ring represented by the formula (I) can be carried out by a process, for instance, comprising suspending a purine derivative having a cyclopropane ring represented by the formula (I) and a catalyst in a solvent to prepare a suspension, and shaking or stirring the resulting suspension in a hydrogen gas atmosphere, or blowing hydrogen gas into the suspension.
Examples of the catalyst include palladium, platinum, nickel, or compounds of one of these elements. Examples of such compounds include hydroxides such as palladium hydroxide; oxides such as platinum oxide; Raney nickel and Raney cobalt; metallic catalysts such as palladium black, platinum black, and the like. Those catalysts may be used alone or they may be used in the form of carrier catalysts in which the catalyst is carried on a carbon, the carrier catalysts including palladium-carbon, platinum-carbon, or the like. Among those catalysts, from the viewpoints of availability and reactivity, palladium-carbon, platinum-carbon, palladium black, palladium hydroxide, and Raney nickel are preferably employed.
It is desired that the amount of the catalyst is 1 part by weight or more, preferably 20 parts by weight or more, more preferably 30 parts by weight or more, based on 100 parts by weight of the purine derivative having a cyclopropane ring represented by the formula (I), in order to expedite the progress of the reaction, and that the amount of the catalyst is 200 parts by weight or less, preferably 100 parts by weight or less, more preferably 50 parts by weight or less, based on 100 parts by weight of the purine derivative having a cyclopropane ring represented by the formula (I), from the viewpoint of economic advantages.
Examples of the solvent include alcohols such as methanol, ethanol, and 2-propanol; ethers such as tetrahydrofuran; organic acids such as acetic acid; esters such as ethyl acetate; polar solvents such as N,N-dimethylformamide; water, and the like. Those solvents may be used alone or in an admixture of two or more kinds.
It is desired that the amount of the solvent is adjusted such that the amount of the purine derivative having a cyclopropane ring represented by the formula. (I) is usually from about 1 to about 100 parts by weight, preferably from about 1 to about 50 parts by weight, more preferably from about 5 to about 30 parts by weight, still more preferably from about 2 to about 10 parts by weight, based on 100 parts by weight of the solvent.
It is desired that the reaction temperature upon catalytic reduction of the purine derivative having a cyclopropane ring represented by the formula (I) is usually from 0xc2x0 to 200xc2x0 C. or so, preferably from 0xc2x0 to 130xc2x0 C. or so, more preferably from 50xc2x0 to 90xc2x0 C. or so, still more preferably from 700 to 90xc2x0 C. or so. In addition, in a case where the suspension of the purine derivative having a cyclopropane ring represented by the formula (I) is shaken or stirred in a hydrogen gas atmosphere, it is desired that the hydrogen gas pressure is usually from 0 to 20 kgf/cm2 or so, preferably from 0 to 10 kgf/cm2 or so, more preferably from 1 to 7 kgf/cm2 or so, still more preferably from 3 to 7 kgf/cm2 or so.
The reaction time cannot be absolutely determined because the reaction time can differ depending upon the reaction temperature, and the like. The reaction time may be preferably a length of time sufficient to terminate the reaction, and the reaction time is usually from 0.5 to 8 hours or so, preferably from 4 to 7 hours or so. The termination of the reaction can be confirmed, for instance, by high-performance liquid chromatography, or the like.
After the termination of reaction, the resulting cyclopropane ring-cleaved purine derivative represented by the formula (X) can be collected by such separation procedures including, for instance, filtration, concentration, extraction, purification, and the like.
On the other hand, in Embodiment (B), the reaction of the purine derivative having a cyclopropane ring represented by the formula (I) with formic acid or a formate can be carried out by a process, for instance, comprising adding a purine derivative having a cyclopropane ring represented by the formula (I) and a catalyst to a solvent, and subsequently adding a formic acid or a formate to the resulting mixture.
As to the catalyst, the same catalysts as those employed in the catalytic reduction in Embodiment (A) can be employed. It is desired that the amount of the catalyst is usually 0.1 parts by weight or more, preferably 10 parts by weight or more, based on 100 parts by weight of the purine derivative having a cyclopropane ring represented by the formula (I), in order to expedite the progress of the reaction, and that the amount of the catalyst is 100 parts by weight or less, preferably 50 parts by weight or less, based on 100 parts by weight of the purine derivative having a cyclopropane ring represented by the formula (I), from the viewpoint of economic advantages.
Examples of the solvent include water; alcohols such as methanol, ethanol, and isopropanol; ethers such as tetrahydrofuran; esters such as ethyl acetate; polar solvents such as N,N-dimethylformamide; and the like. Those solvents may be used alone or in an admixture of two or more kinds. It is desired that the amount of the solvent is adjusted such that the amount of the purine derivative having a cyclopropane ring represented by the formula (I) is from about 1 to about 50 parts by weight, based on 100 parts by weight of the solvent.
Examples of the formate include alkali metal formates such as sodium formate and potassium formate, ammonium formate, triethylammonium formate, and the like. Among them, from the viewpoints of economic advantages, operability, and shortening the reaction time, a preference is given to the alkali metal formates such as sodium formate and potassium formate.
It is desired that the amount of formic acid or the formate is one mol or more, preferably 1.5 mol or more, per one mol of the purine derivative having a cyclopropane ring represented by the formula (I), in order to complete the reaction. It is also desired that the amount of formic acid or the formate is 20 mol or less, preferably 10 mol or less, per one mol of the purine derivative having a cyclopropane ring represented by the formula (I), from the viewpoint of economic advantages.
It is desired that the reaction temperature upon the reaction of the purine derivative having a cyclopropane ring represented by the formula (I) with formic acid or a formate is usually from 0xc2x0 to 150xc2x0 C., preferably from 200 to 80xc2x0 C. In addition, the atmosphere upon reaction is not limited to specified ones, and the atmosphere may be preferably an inert gas atmosphere or a hydrogen gas atmosphere. Incidentally, the reaction is not necessarily carried out in a pressurized reaction system, and the reaction can be carried out under an ambient pressure.
The reaction time cannot be absolutely determined because the reaction time can differ depending upon the reaction temperature, and the like. The reaction time may be preferably a length of time sufficient to terminate the reaction. It is desired that the reaction time is usually from 1 to 20 hours or so, preferably 1 to 10 hours or so. The termination of the reaction can be confirmed, for instance, by the confirmation of the disappearance of the starting materials by high-performance liquid chromatography, or the like.
After the termination of reaction, the resulting cyclopropane ring-cleaved purine derivative represented by the formula (X) can be collected by such conventional separation procedures including, for instance, filtration, concentration, extraction, purification, and the like.
The resulting cyclopropane ring-cleaved purine derivative represented by the formula (X) as prepared above can be further recrystallized from, for instance, 2-propanol, or the like as occasion demands.
A compound where A is xe2x80x94COxe2x80x94 group in the cyclopropane ring-cleaved purine derivative represented by the formula (X) as prepared by the process of the present invention is extremely useful for preparation intermediates for antiviral agents such as Famciclovir and Penciclovir. In addition, a compound where A is xe2x80x94CH2xe2x80x94 group in which a cyclopropane ring-cleaved purine derivative represented by the formula (X) is useful for antiviral agents. In particular, a compound where each of R2 and R3 is acetyl group in the formula (X) is an excellent antiviral agent known as Famciclovir.
Further, according to the present invention, a cyclopropane ring-cleaved compound represented by the formula (XII): 
wherein A is xe2x80x94CH2xe2x80x94 group or xe2x80x94COxe2x80x94 group; B is a nitrogen-containing heterocyclic ring; each of R11 and R12 is independently hydrogen atom, a substituted or unsubstituted alkyl group having 1 to 7 carbon atoms, a substituted or unsubstituted aralkyl group having 7 to 11 carbon atoms, or a substituted or unsubstituted acyl group having 1 to 7 carbon atoms, with proviso that in a case where A is xe2x80x94COxe2x80x94 group, neither R11 nor R12 is a substituted or unsubstituted acyl group having 1 to 7 carbon atoms,
can be prepared by a process comprising reacting a compound having a cyclopropane ring represented by the formula (XI): 
wherein each of X11 and X12 is independently hydrogen atom or a halogen atom; and A, B, R11, and R12 are the same as defined above, with proviso that in a case where in a case where A is xe2x80x94COxe2x80x94 group, neither R11 nor R12 is a substituted or unsubstituted acyl group having 1 to 7 carbon atoms, and each of X11 and X12 is independently a halogen atom,
with formic acid or a formate in the presence of a catalyst.
In the compound having a cyclopropane ring represented by the formula (XI), A is xe2x80x94CH2xe2x80x94 group or xe2x80x94COxe2x80x94 group.
B is a nitrogen-containing heterocyclic ring. The nitrogen-containing heterocyclic ring in the present invention may be, for instance, a modified or unmodified, substituted or unsubstituted purine ring or pyrimidine ring, and the like. Typical examples of the modified or unmodified, substituted or unsubstituted purine ring and pyrimidine ring include purine rings and pyrimidine rings of which hydrogen atom may be substituted by at least one substituent selected from the group consisting of a halogen atom, hydroxyl group, an alkyl group having 1 to 20 carbon atoms, an alkoxy group having 1 to 20 carbon atoms, an aralkyloxy group having 7 to 20 carbon atoms, and a protected or unprotected amino group. Here, examples of the alkyl group having 1 to 20 carbon atoms include methyl group, ethyl group, isopropyl group, and the like. Examples of the alkoxy group 1 to 20 carbon atoms include methoxy group, ethoxy group, cyclohexyloxy group, menthyloxy group, and the like. Examples of the aralkyloxy group having 7 to 20 carbon atoms include benzyloxy group, trityloxy group, and the like.
Concrete examples of the modified or unmodified, substituted or unsubstituted purine ring and pyrimidine ring in the present invention include 2,4-pyrimidinedionyl group, 4-amino-2-pyrimidinonyl group, 5-methyl-2,4-pyrimidinedionyl group, 2-aminopurinyl group, 6-aminopurinyl group, 2-amino-6-hydroxypurinyl group, 2,6-diaminopurinyl group, 2-amino-6-chloropurinyl group, 2-amino-6-iodopurinyl group, 2-amino-6-methoxypurinyl group, 2-amino-6-benzyloxypurinyl group, 2,6-dichloropurinyl group, and the like.
Each of X11 and X12 is independently hydrogen atom or a halogen atom, with proviso that in a case where A is xe2x80x94COxe2x80x94 group, each of X11 and X12 is independently a halogen atom. Examples of the halogen atom include fluorine atom, chlorine atom, bromine atom, and iodine atom, among which a preference is given to chlorine atom, bromine atom, and iodine atom.
Each of R11 and R12 is independently hydrogen atom, a substituted or unsubstituted alkyl group having 1 to 7 carbon atoms, a substituted or unsubstituted. aralkyl group having 7 to 11 carbon atoms, or a substituted or unsubstituted acyl group having 1 to 7 carbon atoms, with proviso that in a case where A is xe2x80x94COxe2x80x94 group, neither. R11 nor R12 is a substituted or unsubstituted acyl group having 1 to 7 carbon atoms.
Examples of the alkyl group having 1 to 7 carbon atoms, preferably an alkyl group having 1 to 6 carbon atoms, include methyl group, ethyl group, propyl group, isopropyl group, 2-methylpropyl group, and the like.
Examples of the aralkyl group having 7 to 11 carbon atoms include benzyl group, and the like.
Examples of the acyl group having 1 to 7 carbon atoms include formyl group, acetyl group, propionyl group, benzoyl group, pivaloyl group, and the like.
Examples of the substituent which may be carried by the alkyl group, the aralkyl group, and the acyl group include alkoxy groups having 1 to 6 carbon atoms, such as methoxy group and phenoxy group; hydroxy group; nitro group; amino group; halogen atoms, such as chlorine atom; cyano group, and the like.
In the formula (XI), it is desired that each of X11 and X12 is independently hydrogen atom, chlorine atom, bromine atom, and iodine atom, and that each of R11 and R12 is independently hydrogen atom, an alkyl group having 1 to 6 carbon atoms, or an acyl group having 1 to 7 carbon atoms.
Typical examples of the compound having a cyclopropane ring represented by the formula (XI) include 2-amino-6-chloro-9-(3,3-dicarbomethoxy-2,2-dichlorocyclopropyl)purine, 2-amino-9-(3,3-dicarbomethoxycyclopropyl)purine, 2-amino-6-chloro-9-3,3-dicarbomethoxycyclopropyl)purine, 2-amino-9-( 3,3-dicarbomethoxy-2,2-dichlorocyclopropyl)-6-methoxypurine, 2-amino-6-benzyloxy-9-(3, 3-dicarbomethoxy-2,2-dichlorocyclopropyl)purine, 2-amino-9-(3,3-dicarbomethoxy-2,2-dichlorocyclopropyl)-6-chloropurine, 2-amino-9-(3,3-dicarboisopropoxy-2,2-dichlorocyclopropyl)-6-chloropurine, and the like.
The compound having a cyclopropane ring represented by the formula (XI) can be prepared by processes described, for instance, in Japanese Patent Laid-Open No. Hei 3-120279 and Japanese Patent Application No. Hei 9-310839.
In the present invention, the reaction of the compound having a cyclopropane ring represented by the formula (XI) with formic acid or a formate can be carried out by a process, for instance, comprising adding a compound having a cyclopropane ring represented by the formula (XI) and a catalyst to a solvent, and adding formic acid or a formate to the resulting mixture.
Examples of the catalyst include palladium, platinum, nickel, or compounds of one of these elements. Those catalysts may be used alone or in admixture of two or more kinds. Examples of compounds of one of those elements include hydroxides such as palladium hydroxide; oxides such as platinum oxide; Raney nickel and Raney cobalt; metallic catalysts such as palladium black, platinum black, and the like. Those catalysts may be used alone or they may be used in the form of carrier catalysts in which the catalyst is carried on a carbon, the carrier catalysts including palladium-carbon, platinum-carbon, or the like. Among those catalysts, from the viewpoints of availability and reactivity, palladium-carbon, platinum-carbon, palladium black, palladium hydroxide, and Raney nickel are preferably employed.
It is desired that the amount of the catalyst is 0.1 parts by weight or more, preferably 10 parts by weight or more, based on 100 parts by weight of the compound having a cyclopropane ring represented by the formula (XI), in order to expedite the progress of the reaction, and that the amount of the catalyst is 100 parts by weight or less, preferably 50 parts by weight or less, based on 100 parts by weight of the compound having a cyclopropane ring represented by the formula (XI), from the viewpoint of economic advantages.
The solvent is not limited to specified ones, and examples thereof include water; alcohols such as methanol, ethanol, and isopropanol; ethers such as tetrahydrofuran; esters such as ethyl acetate; polar solvents such as N,N-dimethylformamide; and the like. Those solvents may be used alone or in an admixture of two or more kinds. It is desired that the amount of the solvent is adjusted such that the amount of the compound having a cyclopropane ring represented by the formula (XI) is from about 1 to about 50 parts by weight, based on 100 parts by weight of the solvent.
One feature of the present invention resides in the use of formic acid or a formate. In the case where formic acid or a formate is used, it is not necessitated to pressurize the reaction system with hydrogen gas as conventionally required, and excellent effects can be exhibited in the efficient hydrogenation of the compound having a cyclopropane ring represented by the formula (XI), so that the desired cyclopropane ring-cleaved compound represented by the formula (XII) can be prepared safely with good operability and in high yield.
Examples of the formate include alkali metal formates such as sodium formate and potassium formate, ammonium formate, barium formate, triethylammonium formate, and the like. Among them, from the viewpoints of economic advantages, operability, and shortening the reaction time, a preference is given to the alkali metal formates such as sodium formate and potassium formate.
It is desired that the amount of formic acid or the formate is one mol or more, preferably 1.5 mol or more, per one mol of the compound having a cyclopropane ring represented by the formula (XI), in order to complete the reaction. It is also desired that the amount of formic acid or the formate is 20 mol or less, preferably 10 mol or less, per one mol of the compound having a cyclopropane ring represented by the formula (XI), from the viewpoint of economic advantages.
In the present invention, the reaction of the compound having a cyclopropane ring represented by the formula (XI) with formic acid or the formate is not necessarily carried out in a pressurized reaction system as described above, but the reaction can be carried out under an ambient pressure.
It is desired that the reaction temperature upon the reaction of the compound having a cyclopropane ring represented by the formula (XI) with formic acid or a formate is usually from 0xc2x0 to 150xc2x0 C., preferably from 20xc2x0 to 80xc2x0 C. In addition, the atmosphere upon reaction is not limited to specified ones, and the atmosphere may be preferably an inert gas atmosphere or a hydrogen gas atmosphere.
The reaction time cannot be absolutely determined because the reaction time can differ depending upon the reaction conditions such as the reaction temperature, and the like. The reaction time may be preferably a length of time sufficient to terminate the reaction. It is desired that the reaction time is usually from 1 to 20 hours or so, preferably 1 to 10 hours or so. The termination of the reaction can be confirmed, for instance, by the disappearance of the starting materials by the confirmation of high-performance liquid chromatography, or the like.
After the termination of reaction, the cyclopropane ring-cleaved compound represented by the formula (XII) can be collected . Therefore, the inorganic salts can be removed from the resulting reaction mixture by a process comprising by conventional separation procedures, including, for instance, filtration, concentration, extraction, purification, and the like.
The resulting cyclopropane ring-cleaved compound represented by the formula (XII) as prepared above can be further recrystallized from, for instance, 2-propanol, or the like as occasion demands.
The resulting cyclopropane ring-cleaved compound represented by the formula (XII) can be favorably used for efficiently preparing preparation intermediates for antiviral agents as disclosed in, for instance, xe2x80x9cNucleoside Nucleotide,xe2x80x9d 15[5] (1996), 981-994; Japanese Examined Patent Publication No. Hei 5-86792, and the like.